By Dr. Peter Mumby, Newcastle University. Source: changingclimate.org, 2003. Read a scientists' personal account of how rising sea temperatures are observably affecting coral ecosystems.

Introduction

Evidence of the devastating impact of climate change on coral reefs is mounting. Hundreds of millions of people around the world rely on these reefs for food and income. Scientists estimate that nearly a third of these precious ecosystems are being destroyed. Some believe even more are at risk from the impacts of climate change. This is a personal account of what one researcher is witnessing and the sense he makes of it as a scientist.

A hard day at the office for Peter Mumby

Sections in this article

Coral bleaching and climate change

What we learnt about coral bleaching

Will there be benefits from climate change?

How the data were collected

Where Next?

 

Coral bleaching and climate change

Coral in a Rangiroa lagoon

One of the main climate issues affecting coral reefs is rising sea temperature. A combination of warm seas and bright sunlight causes "coral bleaching" which can kill corals. Normally coral can recover from these stresses but I was horrified by what I saw happening in 1998 during an El Niño event. The lagoon temperature around the Rangiroa atoll in French Polynesia rose suddenly by a few degrees and within months large areas of the reef died. What is more, a quarter of the normally robust slow growing corals were wiped out in just six months. Interestingly this is one of the few places in the world where they did die so suddenly and we think this is because the warming was sustained and intense.

What troubles us is the rising trend of sea temperatures in this part of the World. In fifty to seventy years normal summer temperatures may be similar to those we saw in 1998 during the El Niño. Unless corals can adapt, it could be the final straw for coral reefs that in many places are already suffering from over-fishing. In the Philippines and Indonesia there is a desperate need for alternative livelihoods because over-fishing has become so acute that reefs are being dynamited to release a catch.

What we learnt about coral bleaching

Our understanding of the bleaching mechanism is growing and this might provide a small ray of hope. For instance, in Tahiti in 1998 there was only a limited amount of bleaching so hardly any coral died. We went to the meteorological office to find out what local weather conditions had been like and discovered that they'd had their cloudiest summer ever. The cloud cover was a buffer. What we've concluded is that if the reefs warm up they are less able to cope with sunlight. Yet in that mechanism there is also evidence that corals can adapt. Microscopic symbiotic algae live in their tissues and give the coral its colour; it is actually these microscopic plants that are killed when the coral is bleached. Some of them can withstand more sunlight than others and coral can change the types of algae in their tissues so there is an avenue of hope if only we can reduce other pressures on our reefs.

Reefs are a tourist attraction in places like Mombasa in Kenya but careless visitors can be another cause of damage.

Will there be benefits from climate change?

Some people ask whether there is a chance that as ocean temperatures change, coral will be able to grow in places that were once too cold. I don't think this is likely because many areas don't favour reefs for other reasons; cloudy water, for instance. It's also not much of a consolation to the many millions of people who currently depend on reefs for their livelihood and food. I think we have to take what is happening as an important warning. When you see something as visually striking as a beautiful haven for diversity being turned into a graveyard it makes you think seriously about climate change.

The reef off Mombasa in Kenya attracts tourists and fishing boats.

We must bear in mind the drastic effects of losing our reefs. They provide new anti cancer drugs being studied by pharmaceutical companies; they are a source of food and exports for many economies; the mainstay of tourism industries often in developing countries, like Kenya; they create sand on tropical beaches also used as a building material; and last but not least they are coastal protection against hurricanes and tropical storms. In Belize in 1998 a reef that took the brunt of the storm mitigated the impact of Hurricane Mitch.

It's very distressing to see a reef change so quickly. I can't think of another ecosystem where climate stress is so obvious.

Starfish and urchins: some of a healthy reef's many diverse inhabitants.

How the data were collected

The scientific monitoring of coral reef deterioration is far more reliable now than it was thirty years ago. Then researchers had to rely on underwater video footage to show the changing reef colour. Obviously this could only provide a snapshot of a small area of reef, was expensive in diver hours and often could only be carried out in less remote locations. For the past thirty years a better picture has been given by remote sensing by satellite but they don't always pick out the subtleties. My colleagues and I have been using an instrument known as CASI (Compact Airborne Spectrographic Imager) that provides a more widespread picture with subtle variations. Our findings appear in the 6^th September 2001 issue of the journal Nature (vol. 413, p36).

Where Next?

On ClimateX.org

Read ‘The Rainbow Unwoven', a scientist's passionate account of a coral bleaching event, and ‘Coral Reefs: their fate in a changing climate', written by a young science write in Oxfordshire.

External Links

The US National Oceanic and Atmospheric Administration (NOAA) Coral Reefs Online is a good site for information and links, as is the main NOAA web site for environment and wildlife news and articles. The Coral Reef Alliance (CORAL) is a non-profit organization working to keep coral reefs alive.

More on changingclimate.org

This article was originally written for a project of the Environmental Change Institute, University of Oxford, called changingclimate.org, which finished in 2003. We have edited this article to make sure that all the links are up to date, but please bear in mind that there will have been some developments since the time of writing.